1. Field of the Invention
The invention relates to a measuring system for contactless detection of a rotational angle, having a first body on which at least one magnet is disposed and having at least one magnetic-field-sensitive element, supported by a second body, for generating a measurement signal, the first body and the second body being rotatable counter to one another about an axis of rotation, and the magnet having a blind-borelike recess.
2. Description of the Prior Art
A measuring system of the type with which this invention is concerned can be used in various systems in the automotive field in which rotational angles have to be measured, such as in a throttle valve transducer, an accelerator pedal value transducer in a pedal module, a vehicle body suspension transducer, or an angle encoder of a windshield wiper drive mechanism.
In such measuring systems, Hall elements are used above all as the magnetic-field-sensitive element. The Hall effect is in the category of galvanomagnetic effects and is evaluated above all by means of thin semiconductor chips. If this kind of semiconductor chip, with current flowing through it, is penetrated at a right angle by a magnetic field, then a voltage proportional to the magnetic field can be picked up transversely to the direction of the current. If silicon is the basic material, signal processing electronics can simultaneously be integrated with the semiconductor chip, making such sensors quite economical. Such integrated Hall ICs are predominantly suitable for measuring angles and distances travelled by detecting the fluctuating field intensity of the magnet that is connected to a moving rotor.
One sensor with such Hall elements is known from European Patent Disclosure EP 1 182 461 A2, for instance; in it, a magnetic field concentrator varies the course in its vicinity of the field lines of the magnet field generated by the magnet and causes the field lines, which in the absence of magnetic field concentrator would extend parallel to the surface of the Hall elements, to penetrate the Hall elements at virtually a right angle to their surface. Hall elements diametrically facing one another each form a pair for generating an output signal, whose intensity depends on the direction of the magnetic field, which in turn is defined by the instantaneous location of the magnet; the magnet is connected in a manner fixed against relative rotation to a rotor, for instance, of an electric motor, and thus on the basis of the output signal, the rotational angle of the rotor can be determined.
Such Hall elements, to make their resolution high enough, require an adequate magnetic field intensity. A high magnetic field intensity also has a favorable effect with regard to extraneous fields and unavoidable ageing. Moreover, these sensors require a homogeneous magnetic angular range so that tolerances for new parts or tolerances that occur in operation, such as shifts in the axis of rotation from wear or mechanical play, can be compensated for. The magnets used in such applications are therefore relatively large.
Some applications, for instance as a rotational angle transducer in accelerator pedal modules, have an adjustment range of from 10. to 30° of angular rotation. In such applications, even small errors, in the range of from 0.1° to 0.3°, cause relatively major changes of voltage in the output signal in the electronics.
A measuring system of this generic kind is know from German Patent Disclosure DE 10 2005 013 442 A1 and is used in an accelerator pedal module. It includes two magnetic disks, located symmetrically to a center axis, each with a blind-borelike recess, between which the magnetic-field-sensitive element is disposed with a relatively large axial air gap. The magnetic field intensity, however, decreases with the distance of the magnetic-field-sensitive element from the magnet. Relatively large magnets are therefore necessary, so as to furnish a sufficient magnetic field intensity and homogeneity for a linear output signal of the magnetic-field-sensitive element.